Processing of ferrophosphorus

ABSTRACT

Ferrophosphorus is heated in admixture and excess aluminum to convert the phosphorus therein to aluminum phosphide. The aluminum phosphide is hydrolyzed and an alloy comprising the nonphosphorus constituents of the ferrophosphorus and unreacted aluminum is separated from the hydrolysis products. The alloy of non-phosphorus constituents and aluminum is useful in the metallurgical industry and the phosphine obtained during the hydrolysis reaction has well-known utility as a chemical intermediate, for example, in preparing gasoline additives such as tributyl phosphine.

United States Patent Scott et al.

[451 Mar. 21, 1972 [54] PROCESSING OF FERROPHOSPHORUS [72] Inventors:Milton J. Scott; Jurgen A. Stenzel, both of St. Louis, Mo.

[73] Assignee: Monsanto Company, St. Louis, Mo.

[22] Filed: Oct. 17, 1969 21 Appl. No.: 867,398

[52] U.S. Cl ..75/129, 23/204, 75/135 [51] Int. Cl. ..C22c 33/00, COlb25/08 [58] Field of Search ..75/129, 132, 135; 23/204 R [56] ReferencesCited UNITED STATES PATENTS 3,423,218 H1969 Gruber ..23/204 X 3,190,7506/1965 Staggers et al. ...75/129 X 1,834,770 12/1931 Lambert ...75/132 X2,966,424 12/1960 Ruehrwein etal ....23/204 OTHER PUBLICATIONSPhosphorus and its Compounds, Vol. I, Science Publishers, Inc., NewYork, page 180.

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-G. K. WhiteAttorney-Herbert B. Roberts, Roger R. Jones, Thomas N. Wallin and NealE. Willis [57] ABSTRACT gasoline additives such as tributyl phosphine.

5 Claims, No Drawings PROCESSING OF FERROPHOSPHORUS BACKGROUND OF THEINVENTION This invention relates to a method of processingferrophosphorus and particularly to a method of separating thenonphosphorus constituents of ferrophosphorus from the phosphoruscontained therein. Ferrophosphorus is a byproduct of the well-knownelectric furnace processes for production of elemental phosphorus.Depending upon the compositions of ore fed to the furnace, theferrophosphorus generally consists of -30 percent phosphorus, from 55-90percent iron and, in some instances, varying amounts of chromium,vanadium, titanium, manganese, nickel and silica. The ferrophosphorus assuch is much less valuable than the individual constituents thereof.Accordingly, methods of separating phosphorus from the non-phosphorusconstituents of ferrophosphorus have been extensively studied but suchmethods have generally proven to be so high in cost as to severely limittheir economic attractiveness. In some instances, known dephosphorizingprocedures convert metallic components to oxides oflimited value.

It has, for some time, been recognized in the industry that aneconomically attractive procedure for processing ferrophosphorus tosegregate the nonphosphorus and phosphorus constituents thereof wouldrepresent a significant contribution to the art.

SUMMARY OF THE INVENTION It is an object of this invention to providemethods of separating phosphorus and nonphosphorus constituents offerrophosphorus into commercially utilizable products.

This is accomplished by heating ferrophosphorus in admixture with excessaluminum to convert the phosphorus therein to aluminum phosphide,hydrolyzing the aluminum phosphide and separating non-phosphorusconstituents from the hydrolysis products as hereinafter described. Theinvention will be better understood from the following description ofthe preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Any of the ferrophosphorusbyproducts commonly obtained in manufacturing elemental phosphorus byelectric furnace processes can be used in the practice of thisinvention. As is known to those familiar with the phosphorus industry,ferrophosphorus is a generic term which designates a mixture of ironphosphides having a composition depending on the composition, the oreand furnace operating conditions. In addition to iron and from 20 topercent, usually 23 to 28 percent by weight phosphorus, theferrophosphorus may contain from small amounts, up to about 6 percentsilicon, up to 10 percent vanadium, up to 10 percent chromium, and minoramounts of other metals such as nickel, manganese and titanium. Theseingredients may be present as phosphides, intermetallic compounds, or inelemental form.

In the process of this invention, the phosphorus content offerrophosphorus is converted to aluminum phosphide by heating theferrophosphorus in admixture with excess aluminum.

The use of high purity aluminum in the practice of this invention is notrequired. Satisfactory results are economically obtained from the use ofaluminum scrap or reclaimed aluminum inasmuch as aluminum oxides andsimilar contaminants present in such material are not found to interferewith the reaction.

It is critical that an excess of aluminum be employed in the practice ofthis invention in order to convert substantially all of the phosphoruscontent of the ferrophosphorus to aluminum phosphide. The exact quantityof aluminum required may vary somewhat depending upon theferrophosphorus composition, however, a quantity exceeding thatstoichiometrically required for conversion of the phosphorus to aluminumphosphide by percent by weight of the nonphosphorus components of theferrophosphorus is generally sufficient to effect substantially completeconversion. As little as 25 percent excess (as defined above) aluminumis sufficient to convert a major portion of the phosphorus values toaluminum phosphide. However, the higher level of unreactedferrophosphorus residue associated with the metal constituents willrender such constituents less valuable when segregated as hereinafterdescribed.

In the practice of the invention, solid aluminum can be added to moltenferrophosphorus, solid ferrophosphorus can be added to molten aluminum,molten ferrophosphorus and aluminum can be intermixed in any order orsolid ferrophosphorus and aluminum can be combined prior to heating.

In order for the conversion of phosphorus to aluminum phosphide to takeplace at an acceptable rate, the mixture must be heated to a temperatureat least sufficient to render the aluminum molten, e.g., about 660 C.Preferably, the mixture will be heated to a temperature at leastsufficient to render substantially the entire system molten. Asrecognized by those skilled in the art, the exact temperature requiredfor the purpose will vary somewhat depending upon the composition of themixture, but temperatures from l,300 to l,500 C. are usually sufficient.There is no theoretical upper temperature limit, however, for reasons ofeconomy temperatures greatly in excess of that required to render themixture molten are generally not considered advantageous.

In order to prevent oxidation of constituents of the mixture, theheating is conducted under an inert atmosphere. The term inert" is usedbroadly to encompass gases not reactive with mixture constituents and isnot limited to totally chemically inert gases. Thus, in addition tohelium, argon, etc., the inert atmosphere can comprise gases such ashydrogen and the like.

Following the reactions described above, the aluminum phosphide ishydrolyzed. This can be conveniently accomplished by cooling the mixture(to prevent unduly vigorous evolution and/or decomposition of phosphine)and introducing it into water. This results in evolution of phosphinegas (heat can be applied to liberate dissolved phosphine, if desired)which can be utilized as an intermediate for preparation of variousorgano phosphine products, leaving a slurry comprising aluminumhydroxide and an alloy of the iron, other nonphosphorus constituents ofthe ferrophosphorus, excess aluminum, and, depending on the quantity ofaluminum utilized, unreacted ferrophosphorus. Alternatively, steam canbe utilized to effect hydrolysis or an acidic or basic solution used toyield soluble hydrogen products. If desired, the aluminum hydroxide canbe conveniently separated by classifiers, effecting separation bydifferences in sedimentation rate of the alloy and aluminum hydroxide.Alternatively, the aluminum hydroxide can be converted to soluble saltsby reaction with acids or bases and the alloy separated by filtration,decantation or the like.

It is generally desired to coalesce the alloy by remelting in thepresence of a flux. The flux may be any material capable of reactingwith or dissolving the aluminum oxide formed during the hydrolysis step.Of course, the flux should be nonreactive with the metal constituents.Suitable fluxes include calcium fluoride, sodium aluminum fluoride,calcium oxide and magnesium oxide. Those skilled in the metal art willrecognize that the ingredients of this alloy render it useful, forexample, as an additive in steel production. The aluminum in the alloyserves as a deoxidant for steel and the chromium and vanadium values aredesirable alloy ingredients for high quality steels. In some instances,a significant phosphorus content in the alloy (which will result fromthe use of less aluminum than required for substantially completephosphorus removal) can be tolerated for specific metallurgicalapplication, e.g., production of phosphorus containing steelscharacterized by reduced ductility.

It is an advantage of this invention that the nonphosphorus ingredientsof the ferrophosphorus are recovered in elemental form rather than asoxides such as produced by many previously known dephosphorizationprocedures.

The practice of the invention is further illustrated by the followingexamples.

EXAMPLE I About 100 grams of ferrophosphorus lumps assaying about 26%phosphorus, about 68.5% iron, about 2% manganese, about 3.45% silica,and about 0.05% nickel is admixed with about 65 grams aluminum.

The mixture is melted to a substantially homogeneous mixture at aboutl,350 C. under a argon atmosphere.

The mix is then cooled and added to excess ice water. There is anevolution of phosphine gas leaving a slurry of metal powder and aluminumhydroxide. The aluminum hydroxide and metal are separated using alaboratory scale sedimentation rate type classifier. The metal assaysabout 65% iron and about 27% aluminum with the balance consisting ofmanganese, silicon, nickel, and less than 1.5% phosphorus.

EXAMPLE II steps of:

a. admixing said ferrophosphorus with a quantity of aluminum exceedingthat stoichiometrically required for conversion of the phosphorus insaid ferrophosphorus to aluminum phosphide by at least 25 percent byweight of the nonphosphorus constituents of said ferrophosphorus,

b. heating the mixture under an inert atmosphere to a temperature of atleast 660 C. and converting phosphorus in said ferrophosphorus toaluminum phosphide, and

c. hydrolyzing said aluminum phosphide.

2. The method of claim 1 wherein the mixture of aluminum andferrophosphorus is heated to a temperature at least sufficient to rendersubstantially the entire mixture molten.

3. The method of claim 2 wherein the aluminum admixed with theferrophosphorus exceeds that stoichiometrically required for conversionof the phosphorus in said ferrophosphorus to aluminum phosphide at 35percent by weight of the nonphosphorus constituents of saidferrophosphorus.

4. The method of claim 3 further comprising the step of separating thenonphosphorus constituents of said ferrophosphorus and unreactedaluminum from the hydrolysis products.

5. The method of claim 4 further comprising the step of coalescing thenonphosphorus constituents of said ferrophosphorus by melting saidconstituents in the presence of a flux.

2. The method of claim 1 wherein the mixture of aluminum andferrophosphorus is heated to a temperature at least sufficient to rendersubstantially the entire mixture molten.
 3. The method of claim 2wherein the aluminum admixed with the ferrophosphorus exceeds thatstoichiometrically required for conversion of the phosphorus in saidferrophosphorus to aluminum phosphide at 35 percent by weight of thenonphosphorus constituents of said ferrophosphorus.
 4. The method ofclaim 3 further comprising the step of separating the nonphosphorusconstituents of said ferrophosphorus and unreacted aluminum from thehydrolysis products.
 5. The method of claim 4 further comprising thestep of coalescing the nonphosphorus constituents Of saidferrophosphorus by melting said constituents in the presence of a flux.